Thickening agents are widely used to assist with swallowing in elderly individuals with impaired swallowing function. High-quality protein intake is recommended for the elderly to prevent malnutrition and frailty. However, the effect of adding thickening agents on the gastric digestion of protein-rich foods has not been sufficiently investigated, raising concerns about their impact on nutrient bioaccessibility. A human gastric digestion simulator (GDS) can quantitatively simulate peristalsis on the gastric wall and visualize the digestion behaviors of food particles. In this study, we investigated the effect of adding thickened aqueous fluid to cooked, minced chicken breast meat rich in protein on in vitro gastric digestibility behavior using GDS.

Sixty grams of minced chicken breast meat was cooked in a microwave oven and used as the control food sample. Food samples were prepared by adding an aqueous fluid (45 g) containing a xanthan gum-based thickener (2.7 or 5.5 wt%) to cooked meat (60 g). Ten milliliters of artificial saliva was added to each food sample, stirred for 1.5 min, and allowed to stand for 30 s to prepare an artificial bolus. Subsequently, an artificial bolus and gastric juice (240 mL, pH 1.3) were introduced into the GDS vessel. An in vitro gastric digestion experiment was conducted at 37 °C for 180 min. The speed and cycle of gastric peristalsis were set to 2.5 mm/s and 1.5 cycles/min, respectively. During digestion, direct observation was performed, and 0.5 mol/L HCl (3 mL) was added every 15 min to adjust the pH of the gastric contents. After the experiment, the gastric digesta was classified using sieves with different mesh sizes (d: 3.35, 2.36, 1.18, and 0.60 mm), and the wet weights of each particle size fraction were measured.

The meat particles gradually disintegrated during gastric digestion in the absence of a thickened fluid, and the release of meat components into the gastric juice was observed. In contrast, the thickened fluid added to heated meat particles partially gelled, which may be attributed to the low pH environment and interactions with cations and proteins in the gastric contents. Moreover, the gel formed adhered to and swelled on the surfaces of meat particles during digestion, suppressing friction between neighboring particles and particle disintegration during digestion. This tendency was particularly pronounced at the high thickener concentration, resulting in a higher retention rate of coarse particles. These results suggest that adding thickened fluid influences digestion behavior in the stomach and that the concentration of thickening agents is an important factor in the design of care foods.

This work was partially supported by the Japan Society Grants-in-Aid for the Promotion of Science (JSPS) KAKENHI Grant Number 24K02892, Japan.